Man-made agents that incorporate multiple copies of both targeting and effector moieties are highly desirable, as they should provide more avid binding and confer enhanced potency. Although recombinant technologies are commonly applied for making fusion proteins with both targeting and effector domains, multimeric structures that comprise the same or different monomeric components to acquire multivalency or multifunctionality may be obtained only with judicious applications of conjugation chemistries.
For agents generated by recombinant engineering, problems may include high manufacturing cost, low expression yields, instability in serum, instability in solution resulting in formation of aggregates or dissociated subunits, undefined batch composition due to the presence of multiple product forms, contaminating side-products, reduced functional activities or binding affinity/avidity attributed to steric factors or altered conformations, etc. For agents generated by various methods of chemical cross-linking, high manufacturing cost and heterogeneity of the purified product are two major limitations.
Thus, there remains a need in the art for a general method of making multivalent structures of multiple specificities or functionalities, which are of defined composition, homogeneous purity, and unaltered affinity, and can be produced in high yields without the requirement of extensive purification. Furthermore, such structures must also be sufficiently stable in serum to allow in vivo applications. A need also exists for stable, multivalent structures of multiple specificities or functionalities that are easy to construct and/or obtain in relatively purified form.